Power

Long ago, Jeff Garvey, city employee, explained it to me: people who stay in government aren't motivated by money -- they're motivated by power.

Now notes Glen Reynolds: "My historian-brother often says that one of the most interesting phenomena that he's observed is the cross-cultural willingness of people to trade away economic benefits for status. I suspect that this is one example of that. So, in a surprisingly similar way, is being a politician."

Thomas Sowell defines economics as the study of the allocation of scarce resources. Okay. That works.